Meta Decorator

Motivation

I often have lots of small schemas containing unique Meta classes with only a few attributes. The Meta class sometimes requires more lines than the schema definition and makes a file containing multiple schemas harder to read. This is especially true when using marshmallow-jsonapi due to type_.

Proposal

Provide a meta decorator that will inject its kwargs into a Meta class for the class it is wrapping.

Example

Before:

class TestSchema(Schema):
    foo = fields.String()
    bar = fields.String()

    class Meta:
        type_ = 'tests'
        ordered = True

After:

@meta(type_='tests', ordered=True)
class TestSchema(Schema):
    foo = fields.String()
    bar = fields.String()

[deckar01]

Inheritance is another good use case where Meta is likely to only need a few attributes. I was initially imagining spreading the parent meta manually like @meta(..., **vars(ParentSchema.Meta)), but that doesn’t actually work. Implicitly inheriting into a new class would be convenient.

A use case for stacking might be if you have enough attributes to justify a meta class, but still preferred the decorator syntax. It would avoid opening and indenting the meta arguments into a block (which a linter might do automatically).

@meta(
    type_='tests',
    include=['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'I', 'j', 'k', ...],
)
class TestSchema(Schema):
    foo = fields.String()
    bar = fields.String()

@meta(type_='tests')
@meta(include=['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'I', 'j', 'k', ...])
class TestSchema(Schema):
    foo = fields.String()
    bar = fields.String()

[deckar01]

I published a module for this functionality. I think this should just be a community library for now. Once I cover it with tests I will add it to the wiki and close this issue.

https://github.com/deckar01/marshmallow-meta